Mechanical belt fasteners are widely employed in a variety of conveyor belting applications for splicing ends of conveyor belts together. There are hinged fastener systems that have fasteners with upper and lower plates joined by arcuate loops. The plates have apertures therein with respective apertures in the upper and lower plates being aligned so that fastener members, e.g. nails, staples, bolts, rivets, can be installed through the apertures and the belt for clamping the plates on the corresponding belt upper and lower surfaces. With the hinged fasteners so attached, the loops project beyond the belt end for cooperating with loops of similar fasteners attached on another belt end to form a passageway through the mating loops for receiving a hinge pin therethrough.
There are a number of hinged fastener systems available. In selecting hinged fasteners, a number of factors are taken into consideration. Choosing an appropriate hinged fastener for a conveyor system requires taking into account the tensile strength of the belts employed and the pulley diameters in the conveyor drive system on which the belt is to be run. One inch wide samples of belts are subjected to dumbbell tests by belt manufacturers with their breakage point measured to determine their UTL (ultimate tensile strength). The fasteners are rated by their PIW (pounds per inch of width) that they can withstand before failure, with an appropriate safety factor, i.e. 4:1, included in their PIW rating. Belt fastener manufacturers provide recommended usages for their particular fasteners so that the fasteners do not fail at high pull-out or tension forces before the belt gives way to applied tension at its splice such as by belt breakage or comb out of the fasteners through the belt material. Fastener manufacturers also provide guidelines for the hinged belt fastener that should be selected for travel over the smallest pulley in the conveyor drive system.
As is apparent, a major goal of belt fasteners is to provide the fastener with strong holding capacity without over design of the fastener for its particular conveyor application, which can range from light-weight assembly line and check-out counter applications to medium and heavy-duty applications such as in underground mines and in aggregate plants. An over-designed fastener can have plates that are too thick and have a higher profile than necessary for the belts with which they are designed to be used which can create problems in travel of the spliced belt about smaller pulleys and with scraper blades used for cleaning the belts. On the other hand, it is generally understood that the larger the plates of the fastener and the greater the reachback of the fastener plates onto the belt surface, the higher durability and strength of the gripping and holding force of the fastener on the belt end. A fastener's reachback is typically determined by the distance from the belt stop thereof against which the end of the belt is abutted and the outboard edges of the fastener plates. Thus, proper abutment of the belt end with the belt stop before attaching the fasteners to belt ends maximizes the reachback of the fasteners and thus their holding power.
With respect to rivet-hinged fasteners, their holding power is generally improved as greater numbers of rivets are utilized, such as three or five rivets over a two rivet fastener. However, the greater number of rivets increases the size of the plates so that both the higher number of rivets and larger plates drives up the cost for the belt fasteners making the fastener more expensive than is desirable. Accordingly, a less expensive, smaller fastener, e.g. a two rivet fastener, that provides strong holding power such as comparable to that provided by three rivet fasteners for medium duty applications would be desirable. As mentioned, such a smaller fastener would also provide advantages in terms of its lower profile and ability to travel over small diameter pulleys.
It is known to use teeth that are bent down from an upper plate of a hinge fastener for improved holding power. The assignee herein has bolt hinged fasteners where a single high strength bolt is used to attach the fastener onto a belt end. Teeth are bent from the side of one of the plates so that the teeth are generally perpendicular to the edge or end of the belt. The above-described teeth are effective to provide the bolt hinged fastener with improved holding capacity; however, with the perpendicular arrangement of the teeth relative to the belt end, they are more likely to serve as a knife edge cutting through the belt material under high applied tensile forces. Accordingly, better designed teeth that are more resistant to being pulled through the belt material under tensile loads would be desirable.
If splices of conveyor belts fail during conveying operations, abrupt shutdowns can occur potentially causing damage to the conveying system and products conveyed thereby and creating safety hazards. In addition, such shutdowns can require expensive repairs and lead to lengthy downtimes lowering productivity. Thus, a conveyor splicing system that provides an early warning as to potential splice failures would be desirable so that conveyor operators or workers get a visual indication of the beginning of splice stress and fatigue, i.e. pull-off of the belt end from the fastener belt stops, before the splice fails. In this manner, the workers are afforded an opportunity to shut down the conveyor line and perform necessary repairs without the sudden conveyor shutdown occasioned by belt splice failure.
Another feature of present belt fasteners that assists in providing good holding power and a low profile fastener attached onto the belt end is that the outer or outboard edges of the plates are generally beveled or coined so that when the plates of the fastener are clamped to the belt surfaces, the sharp edges of the plates will bite into the belt surface. Generally, the outboard edges extend straight across the plate parallel to the end of the belt with rivet apertures spaced back from this straight edge. Where there are a pair of apertures adjacent the straight outboard edge, it has been found that there is too much material spaced from the apertures for the belt edge to get a good grip or bite into the belt. Accordingly, there is a need for a fastener with improved belt gripping at the outboard edges thereof.
Another consideration in the design of hinged rivet belt fasteners is that they should be compatible for use with existing installation tools. There is a commercially available installation tool provided by the assignee herein which is for gang driving of all five rivets of a five-rivet fastener simultaneous. This is accomplished by use of a gang driver whose multiple drive rods are inserted into through holes in a guide block for driving the rivets towards a lower anvil plate of the tool and setting the lower ends of the rivets against raised rivet head forming bushings aligned with the rivet guide holes in the guide block which match the five rivet pattern of the fastener. Where the fastener uses less than five rivets such as the preferred two rivet fastener herein, there will be raised bushings that are not necessary for forming rivet heads. Accordingly, the plates of rivet-hinged fasteners, and particularly the lower plates thereof should be capable of insertion over the anvil plate while accommodating and clearing any raised bushings that are not used for setting rivet heads so that the smaller fastener herein can be used in current five rivet-hinged fastener installation tools.